1. Field of the Invention
The present invention relates to a combined knob and permutation lock assembly for door latches and, more particularly, to a permutation lock assembly designed to fit conventional swinging doors to provide maximum security without the need of a key which could be lost, stolen, or duplicated.
2. Description of the Prior Art
Conventional swinging doors typically include a combined knob and key lock assembly for activating the door latch. Such combined knob and key lock assemblies are readily installed in a door by drilling a single circular hole through the door and by drilling a second hole perpendicular to the first hole for the latch assembly. Thus, such a construction is readily securable to a door and provides a reasonable degree of security, under normal circumstances.
The main problem with such a combined knob and key lock assembly is the need for a key to unlock the door from the outside thereof. Such keys can be lost, stolen, or duplicated, and the keyhole presents an opening for tampering with the lock mechanism. If the key is lost or stolen, the procedure for changing the combination typically requires the intervention of a skilled locksmith and the high cost associated therewith.
One common approach to solving the problem of lost keys for locks in general is the use of a permutation-type lock assembly. With a permutation-type lock, keys may be eliminated, thereby eliminating the problems associated with the loss thereof. However, while permutation-type locks are generally well known, they are not generally known for use in combination with a door knob to operate a door latch.
U.S. Pat. Nos. 724,774; 1,076,171; 1,217,802; 1,287,435; 1,554,270; 1,816,575; and 2,836,052 disclose permutation lock assemblies for use with a swinging door. However, all of such mechanisms have at least one of several problems associated therewith. In some of these mechanisms, the entire lock assembly is external to the door where it is unattractive and readily available for tampering or destruction. Others of said mechanisms require substantial modification to the normal door apertures or the addition of separate and distinct locking elements different from the conventional door latch. Heretofore, it has been unknown to provide a combined knob and permutation lock assembly designed to fit conventional swinging doors without any modification thereto for use with conventional door latches to provide maximum security without the need of a key which could be lost, stolen, or duplicated.